Preparation Of Doped Co/CeO₂Catalysts And Their Catalytic Performances Of Ethanol Steam Reforming For Hydrogen Production

Ethanol is a widely available, clean liquid fuel with high content of hydrogen.Hydrogen production from ethanol steam reforming has the advantages of highefficiency and environmental benignity, which could be applied to supply hydrogenfor proton exchange membrane fuel cell.This work prepared Ca-doped Co/CeO₂catalysts using citric acid complexingmethod and Ni-doped Co/CeO₂catalysts with coprecipitation. The catalysts werecharacterized with low temperature N2adsorption （BET）, X-ray diffraction （XRD）,temperature programmed reduction in hydrogen （H2-TPR）, Fourier TransformInfrared （FTIR）, high resolution transmission electronic microscope （HR-TEM） andthermal gravity （TG） at the different state. The catalytic performances for ethanolsteam reforming and initial stability were also investigated and the followingresults were obtained.（1） For Ca-doped Co/CeO₂catalysts prepared by citric acid complexing, part ofCo³⁺was incorporated into CeO₂lattice, showing a strong interaction with support,which resulted in the formation of Co-O-Ce bond and easier reduction of Co³⁺.Suitable content of Ca-doping also benefited the formation of CeO₂with smallerparticle size of CeO₂of around15.0nm. However, Ca-doping would reduce theinteraction of metal and support, making the Co³⁺in the lattice of CeO₂hard toreduce.（2） Ce/CeO₂catalyst showed good performance for ethanol steam reforming at400⁵00℃, Ca-doped catalysts showed no obvious advantage. However, at550⁶50℃,5.0wt%Ca-doped catalyst could efficiently improve the selectivity ofhydrogen, hydrogen yield of85.2%was obtained at working conditions of T=550℃,P=101kPa, H2O/C2H5OH=6.0and GHSV=50,000mL·g^-1·h^-1, while catalysts withover5.0wt%Ca-doping resulted in worse performances.（3） Catalyst stability of Co0.1Ce0.9Oyand Co0.1Ce0.85Ca0.05Oywas initiallyinvestigated for50.0h. The results indicated that both catalysts showed good initialstability. The HR-TEM and TG characterization of the utilized catalysts suggested that5.0wt%Ca-doping efficiently reduced the carbon content on the surface ofcatalyst, which could be ascribed to the enhanced oxygen storage capacity of CeO₂and smaller particle size of CeO₂after Ca-doping. The carbon deposited upon thecatalyst surface could be removed under steam reforming working conditions.（4） To improve the low temperature catalytic activity, Ni-doped Co/CeO₂catalysts were prepared by coprecipitation. Ni-doping resulted in lower temperaturefor reduction of Co³⁺, Ce⁴⁺and Ni²⁺, indicating that interaction between Ni and Co.6.0wt%Ni-doping resulted in best catalytic performances for ethanol steamreforming, ethanol conversion of100.0%and hydrogen yield of56.0%wereobtained under working conditions of T=450℃, P=101kPa, H2O/C2H5OH=6.0andGHSV=50,000mL·g^-1·h^-1. Initial stability investigation of50.0h suggested itsgood stability. TG characterization of the utilized catalyst suggested higher contentof carbon deposition over Ni-Co/CeO₂than Co/CeO₂catalyst.